Am 31.08.2016 um 21:07 schrieb William F Pokorny:
> On 08/31/2016 01:16 PM, clipka wrote:
>> Am 31.08.2016 um 16:12 schrieb William F Pokorny:
>>
>>> A - POV-Ray 3.7.0.unofficial
>>>
>>> B - POV-Ray 3.7.1-alpha.8764097.unofficial (current 3.7.1)
>>>
>>> C - POV-Ray 3.7.1-alpha.8738139.unofficial (refactor/texture)
>>>
>>> Is showing differences in all three when run with radiosity. See the
>>> attached image where A, B and C shown left to right.
>>>
>>> If run without radiosity A & C match well, but our current 3.7.1 is
>>> still different.
>>>
>>> If run without radiosity and finish statements A, B & C match well, so
>>> something is different in finish {} with our current 3.7.1.
>>>
>>> Unsure what might be expected and not. Where would you like to go from
>>> here?
>>
>> Just to make sure -- you're saying that the version to be tested (the
>> refactor/texture one) matches good old 3.7.0, while the current version
>> that you used as reference shows differences?
> 
> Only with radiosity off does the re-factored code match 3.7.0 -
> otherwise none of the three match exactly.

That is to be expected, unless you choose particularly high-quality
settings.

You can also increase the chances of identical results by using the
`+HR` command-line switch.

> I'm also not sure if the aim is to always exactly match 3.7.0? In the
> case of media for example, we know we don't match 3.7.0 to 3.7.1, but we
> are happier with the 3.7.1 result.

Yes, but there's a reason why we threw backward compatibility overboard
(to some degree) and changed the media code: The old implementation had
a bug, and computed demonstrably wrong results for low quality settings.
The implementation obviously failed to match the intention.

There is no reason (or at least none that I'm currently aware of) to
think that there is a similar problem with the 3.7.0 finish
computations. One might debate whether the shading models chosen by the
original developers are a good choice (spoiler alert: I think they are
reasonably good, except for the "brilliance" parameter), but their
implementation seems to be correct. The implementation does seem to
match the intention.

Post a reply to this message